Network Working Group G. Giaretta
Request for Comments: 5637 Qualcomm
Category: Informational I. Guardini
E. Demaria
Telecom Italia
J. Bournelle
Orange Labs
R. Lopez
University of Murcia
September 2009
Authentication, Authorization, and Accounting (AAA) Goalsfor Mobile IPv6
Abstract
In commercial and enterprise deployments, Mobile IPv6 can be a
service offered by a Mobility Services Provider (MSP). In this case,
all protocol operations may need to be explicitly authorized and
traced, requiring the interaction between Mobile IPv6 and the AAA
infrastructure. Integrating the Authentication, Authorization, and
Accounting (AAA) infrastructure (e.g., Network Access Server and AAA
server) also offers a solution component for Mobile IPv6
bootstrapping. This document describes various scenarios where a AAA
interface for Mobile IPv6 is required. Additionally, it lists design
goals and requirements for such an interface.
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
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RFC 5637 AAA Goals for Mobile IPv6 September 2009
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Table of Contents
1. Introduction ....................................................32. Terminology .....................................................33. Motivation ......................................................44. Bootstrapping Scenarios .........................................44.1. Split Scenario .............................................54.2. Integrated Scenario ........................................65. Goals for AAA-HA Interface ......................................65.1. General Goals ..............................................65.2. Service Authorization ......................................75.3. Accounting .................................................85.4. Mobile Node Authentication .................................85.5. Provisioning of Configuration Parameters ...................86. Goals for the AAA-NAS Interface .................................97. Security Considerations .........................................98. Acknowledgements ................................................99. References .....................................................109.1. Normative References ......................................109.2. Informative References ....................................10Giaretta, et al. Informational [Page 2]

RFC 5637 AAA Goals for Mobile IPv6 September 20091. Introduction
Mobile IPv6 [1] provides the basic IP mobility functionality for
IPv6. When Mobile IPv6 is used in tightly managed environments with
the use of the AAA (Authentication, Authorization, and Accounting)
infrastructure, an interface between Mobile IPv6 and AAA protocols
needs to be defined. Also, two scenarios for bootstrapping Mobile
IPv6 service [2], i.e., split [3] and integrated [6] scenarios,
require the specification of a message exchange between the Home
Agent (HA) and AAA infrastructure for authentication and
authorization purposes and a message exchange between the AAA server
and the NAS in order to provide the visited network with the
necessary configuration information (e.g., Home Agent address).
This document describes various scenarios where a AAA interface is
required. Additionally, it lists design goals and requirements for
the communication between the HA and the AAA server and between the
NAS and the AAA server needed in the split and integrated scenarios.
Requirements are listed in case either IPsec or RFC 4285 [4] is used
for Mobile IPv6 authentication.
This document only describes requirements, goals, and scenarios. It
does not provide solutions.
Notice that this document builds on the security model of the AAA
infrastructure. As such, the end host/user shares credentials with
the home AAA server and the communication between the AAA server and
the AAA client may be protected. If the AAA server and the AAA
client are not part of the same administrative domain, then some sort
of contractual relationship between the involved administrative
domains is typically in place in the form of roaming agreements.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [5], with the
qualification that, unless otherwise stated, these words apply to the
design of the AAA protocol extension, not its implementation or its
usage.
The following terms are extracted from [2].
o Access Service Authorizer (ASA). A network operator that
authenticates a Mobile Node and establishes the Mobile Node's
authorization to receive Internet service.
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RFC 5637 AAA Goals for Mobile IPv6 September 2009
o Access Service Provider (ASP). A network operator that provides
direct IP packet forwarding to and from the end host.
o Mobility Service Authorizer (MSA). A service provider that
authorizes Mobile IPv6 service.
o Mobility Service Provider (MSP). A service provider that provides
Mobile IPv6 service. In order to obtain such service, the Mobile
Node must be authenticated and prove authorization to obtain the
service.
3. Motivation
Mobile IPv6 specification [1] requires that Mobile Nodes (MNs) are
provisioned with a set of configuration parameters -- namely, the
Home Address and the Home Agent Address, in order to accomplish a
home registration. Moreover, MNs and Home Agents (HAs) must share
the cryptographic material needed in order to set up IPsec security
associations to protect Mobile IPv6 signaling (e.g., shared keys or
certificates). This is referred as the bootstrapping problem: as
described in [2], the AAA infrastructure can be used as the central
element to enable dynamic Mobile IPv6 bootstrapping. In this case,
the AAA infrastructure can be exploited to offload the end host's
authentication to the AAA server as well as to deliver the necessary
configuration parameters to the visited network (e.g., Home Agent
address as specified in [6]).
Moreover, in case Mobile IPv6 is a service offered by a Mobility
Service Provider (MSP), all protocol operations (e.g., home
registrations) may need to be explicitly authorized and monitored
(e.g., for accounting purposes). This can be accomplished relying on
the AAA infrastructure of the Mobility Service Authorizer (MSA) that
stores user profiles and credentials.
4. Bootstrapping Scenarios
This section describes some bootstrapping scenarios in which
communication between the AAA infrastructure of the Mobility Service
Provider and the Home Agent is needed. The need of MIPv6-aware
communication between the AAA server and the Network Access Server
(NAS) is also described. The purpose of this section is only to
explain the situation where bootstrapping is required. The actual
mechanisms and additional details are specified elsewhere or are left
for future work (see, e.g., [2], [3], and [6]).
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RFC 5637 AAA Goals for Mobile IPv6 September 20094.1. Split Scenario
In the split scenario [3], there is the assumption that the mobility
service and network access service are not provided by the same
administrative entity. This implies that the mobility service is
authorized by the MSA that is a different entity from the ASA.
In this scenario, the Mobile Node discovers the Home Agent Address
using the Domain Name Service (DNS). It queries the address based on
the Home Agent name or by service name. In the former case, the
Mobile Node is configured with the Fully Qualified Domain Name (FDQN)
of the Home Agent. In the latter case, [3] defines a new service
resource record (SRV RR).
Then the Mobile Node performs an IKEv2 [7] exchange with the HA to
set up IPsec Security Associations (SAs) to protect Mobile IPv6
signaling and to configure its Home Address (HoA). Mutual
authentication for IKEv2 between Mobile Node and Home Agent can be
done with or without use of the Extensible Authentication Protocol
(EAP).
If EAP is used for authentication, the operator can choose any
available EAP methods. Use of EAP with the AAA infrastructure allows
the HA to check the validity of each MN's credentials with the AAA
infrastructure, rather than having to maintain credentials for each
MN itself. It also allows roaming in terms of Mobile IPv6 service
where the MSP and MSA belong to different administrative domains. In
this case, the HA in the MSP can check the validity of the
credentials provided by the MN with the AAA infrastructure of MSA,
receiving the relevant authorization information.
The Mobile Node may also want to update its FQDN in the DNS with the
newly allocated Home Address. [3] recommends that the HA performs the
DNS entry update on behalf of the Mobile Node. For that purpose, the
Mobile Node indicates its FDQN in the IKEv2 exchange (in the IDi
field in IKE_AUTH) and adds a DNS Update Option in the Binding Update
message sent to the HA.
When the Mobile Node uses a Home Agent belonging to a different
administrative domain (MSP != MSA), the local HA may not share a
security association with the home DNS server. In this case, [3]
suggests that the home AAA server is responsible for the update.
Thus, the HA should send to the home AAA server the (FDQN, HoA) pair.
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RFC 5637 AAA Goals for Mobile IPv6 September 20094.2. Integrated Scenario
In the integrated scenario, the assumption is that the Access Service
Authorizer (ASA) is the same as the Mobility Service Authorizer
(MSA). Further details of this type of a scenario are being worked
on separately [6].
The Home Agent can be assigned either in the Access Service
Provider's network or in the separate network. In the former case,
the MSP is the same entity as the ASP, whereas in the latter case the
MSP and ASP are different entities.
In this scenario, the Mobile Node discovers the Home Agent Address
using DHCPv6. If the user is authorized for Mobile IPv6 service,
during the network access authentication the AAAH (the AAA server in
the home network) sends the information about the assigned Home Agent
to the NAS where the Mobile Node is currently attached. To request
Home Agent data, the Mobile Node sends a DHCPv6 Information Request
to the All_DHCP_Relay_Agents_and_Servers multicast address. With
this request, the Mobile Node can specify if it wants a Home Agent
provided by the visited domain (ASP/MSP) or by the home domain
(ASA/MSA). In both cases, the NAS acts a DHCPv6 relay. When the NAS
receives the DHCPv6 Information Request, it passes Home Agent
information received from the AAAH server to the DHCP server, for
instance using mechanisms defined in [6].
In case the Mobile Node cannot acquire Home Agent information via
DHCPv6, it can try the default mechanism based on DNS described in
[3]. After the Mobile Node has acquired the Home Agent information,
the mechanisms used to bootstrap the HoA, the IPsec Security
Association, and the authentication and authorization with the MSA
are the same as described in the bootstrapping solution for the split
scenario [3].
5. Goals for AAA-HA InterfaceSection 4 raises the need to define extensions for the AAA protocol
used between the AAA server of the MSA and the HA. The following
sections list the goals for such an interface. This communication is
needed for both the split and integrated scenarios.
5.1. General Goals
G1.1 The communication between the AAAH server and the HA MUST reuse
existing AAA security mechanisms with regard to authentication,
replay, integrity, and confidentiality protection. These
communication security mechanisms prevent a number of classical
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RFC 5637 AAA Goals for Mobile IPv6 September 2009
threats, including the alteration of exchanged data (e.g.,
Mobile IPv6 configuration parameters) and the installation of
unauthorized state.
5.2. Service Authorization
G2.1 The AAA-HA interface MUST allow the use of a Network Access
Identifier (NAI) to identify the user.
G2.2 The HA MUST be able to query the AAAH server to verify Mobile
IPv6 service authorization for the Mobile Node.
G2.3 The AAAH server MAY assign explicit operational limitations and
authorization restrictions on the HA (e.g., packet filters, QoS
parameters).
G2.4 The AAAH server MUST be able to send an authorization lifetime
to the HA to limit Mobile IPv6 session duration for the MN.
G2.5 The HA MUST be able to request that the AAAH server grant an
extension of the authorization lifetime to the MN.
G2.6 The AAAH server MUST be able to force the HA to terminate an
active Mobile IPv6 session for authorization policy reasons
(e.g., credit exhaustion).
G2.7 The HA MUST be able to indicate to the AAAH server the IPv6 HoA
that will be assigned to the MN.
G2.8 The AAAH server MUST be able to authorize the MN to use an IPv6
HoA and MUST indicate that to the HA.
G2.9 The AAAH server MUST be able to indicate to the HA whether or
not the return routability test (HoT (Home Test) and HoTi (Home
Test Init)) shall be permitted via the HA for a given MN.
G2.10 The AAAH server MUST be able to support different levels of
Mobile IPv6 authorization. For example, the AAAH server may
authorize the MN to use MIPv6 (as defined in [1]) or may
authorize the MN to utilize an IPv4 HoA assigned for Dual Stack
MIPv6 [8].
G2.11 The AAAH server MUST be able to indicate to the HA whether the
bearer traffic for the MN needs to receive IPsec Encapsulating
Security Payload (ESP) protection.
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RFC 5637 AAA Goals for Mobile IPv6 September 2009
G2.12 The HA MUST be able to authenticate the MN through the AAAH
server in case a pre-shared key is used in IKEv2 for user
authentication. The exact procedure is part of the solution
space.
5.3. Accounting
G3.1 The AAA-HA interface MUST support the transfer of accounting
records needed for service control and charging. These include
(but may not be limited to): time of binding cache entry
creation and deletion, octets sent and received by the Mobile
Node in bi-directional tunneling, etc.
5.4. Mobile Node Authentication
G4.1 The AAA-HA interface MUST allow the HA to act as a pass-through
EAP authenticator.
G4.2 The AAA-HA interface MUST support authentication based on the
Mobility Message Authentication Options defined in [4].
G4.3 The AAAH server MUST be able to provide a MN-HA key (or data
used for subsequent key derivation of the MN-HA key by the HA)
to the HA if requested. Additional data, such as the Security
Parameter Index (SPI) or lifetime parameters, are sent along
with the keying material.
G4.4 The HA supporting the Authentication Protocol MUST be able to
request that the AAAH server authenticate the MN with the value
in the MN-AAA Mobility Message Authentication Option.
G4.5 The HA MUST include an identifier of the Mobile Node in the AAA
transactions with the AAAH server.
5.5. Provisioning of Configuration Parameters
o The HA SHOULD be able to communicate to the AAAH server the Home
Address allocated to the MN and the FQDN of the MN (e.g., for
allowing the AAAH server to perform a DNS update on behalf of the
MN).
o The AAAH server SHOULD be able to indicate to the HA if the MN is
authorized to autoconfigure its Home Address. If the AAAH does
not indicate to the HA if a MN is authorized to autoconfigure its
address, the MN is not authorized.
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RFC 5637 AAA Goals for Mobile IPv6 September 20096. Goals for the AAA-NAS Interface
In the integrated scenario, the AAA server provides the HA
information to the NAS as part of the whole AAA operation for network
access.
G6.1 The AAAH server MUST be able to communicate the Home Agent
Information (IP address or FQDN) to the NAS.
G6.2 The NAS MUST be able to notify the AAAH server if it supports
the AAA extensions designed to receive the HA assignment
information.
G6.3 The ASP/MSP supporting the allocation of a Home Agent MUST be
able to indicate to the MSA if it can allocate a Home Agent to
the MN. Therefore, the NAS MUST be able to include a suggested
HA address in the ASP in the AAA-NAS interaction.
G6.4 The AAA server of the MSA MUST be able to indicate to the NAS
whether the MN is authorized to use a local Home Agent (i.e., a
Home Agent in the ASP/MSP).
G6.5 The overall AAA solution for the integrated scenario MUST
support the scenario where the AAA server of the ASA/MSA used
for network access authentication is different from the AAA
server used for mobility service authentication and
authorization.
7. Security Considerations
As stated in Section 5.1, the AAA-HA interface must provide mutual
authentication, integrity, and replay protection. Furthermore, if
security parameters (e.g., IKE pre-shared key) are transferred
through this interface, confidentiality is strongly recommended to be
supported. In this case, the links between the HA and the AAA server
of the MSA and between the NAS and the AAA server MUST be secure.
8. Acknowledgements
The authors would like to thank James Kempf, Alper Yegin, Vijay
Devarapalli, Basavaraj Patil, Gopal Dommety, Marcelo Bagnulo, and
Madjid Nakhjiri for their comments and feedback. Moreover, the
authors would like to thank Hannes Tschofenig for his deep technical
and editorial review of the document. Finally the authors would like
to thank Kuntal Chowdhury who contributed by identifying the goals
related to RFC 4285 authentication.
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